Time lag fuse



Sept 22,1942 G. R. BROWN 2,296,627

TIME LAG FUSE Filed 001'.. 30, 1937 Inventor: George R. Brown,

Hi e Attorney.

Patented sept. 22, i942 'rma LAG rosa f" vcomo n. Brown, Stratford, com,minor to General Electric Company, a corporation of New York Applicationootobor so, i931, sorua No. 111,940

' (ci. zoo-123) 6 Claims.

This invention relates to time lag fuses for use in circuits which aresubject to' a partial overload for a brief period of time.

It is an object of the invention to provide a time lag fuse which willwithstand for a brief period a partial overload of the circuit withwhich' it is connected, but which will blow if the overload is continuedbeyond this brief period, and which, in addition, will blow immediatelyif subjected to a heavy overload such as that produced by a shortcircuit.

Referring to the drawing, Fig. 1 isa longitudi- .nal section through thefuse; Fig. 2 is an exploded view of some of th'e fuse parts, and Fig. 3shows a modified formof construction of one end of the fuse.

The fuse comprises a tubular insulating casing ID which may be formed ofliber, or the like, and carries at each end metal ferrules II which areclamped to the ends of the tube and serve to make contact with thecircuit in which the fuse is inserted. A fuse link I2 is inserted withinthe casing and occupies the right-hand portion thereof as shown byFig. 1. The fuse link is fastened at one end to the ferrule I I bysolder I3 and at the other end to a tab I4 by means of solder I5 havinga relatively high melting point, for example, 360 F. The tab I4 islanced from a plug I6 which may be formed of copper, or the like, and

which has a relatively large mass formed with The fuse link has a olarge radiating surfaces. blow point I'I formed immediately adjacent thecopper plug, so that as it is heated by a partial overload the heat willbe absorbed by the copper plug I6 to prevent melting of the fuse link atthe blow point. The heat absorbed by the copper plug is dissipated byvirtue of its large mass and radiating surfaces.

The plug I6 rests against an inner tube lof insulating material, theinner tube being nested within the tube I at its left-hand portion asshown by Fig. 1, and being retained therein by the other ferrule I I. Abrass cup I9 is inserted within a recess forming part of the copper plugI6 and holds a disk 2l in the bottom of the recess 20 where it covers anopening 22 formed in the wall of the copper plug at the point where thetab I4 is lanced therefrom. The disk 2I is formed from asbestos paper,or the like, and is adapted to hold a iiller material 23 coniined aboutthe fuse link I2 'and prevent its sifting past the plug I6. The

brass cup I9 is fastened to the copper plug I6 by solder 24 having arelatively low melting point, for example, 220 F. The solder is disposedabout the entire periphery of the cup I9- and recess 20, 55

in the manner shown by Fig. 1 and holds the cup I9 securely within therecess 2Il'where it retains the disk 2I in the bottom of the recess.

The brass cup I9 has a tab 25 lanced from the end wall thereof which isprovided with an opening 26 adapted to receive one end of a coil spring21, the other end of the spring being secured to the ferrule II by meansoi.' solder 28. The spring is placed under tension and acts to' hold theplug I6 tightly against the inner tube I8. A conducting cable 29 issoldered to the tab 25 at one end and to the ferrule II atthe other end.This cable is formed' of stranded copper wire which has a low resistanceand, consequently, there is a low voltage drop or watt loss through thefuse circuit. The inner tube I8 forms an expansion chamber 30 whichhouses the spring 21 and cable 29 and which is closed at its outer endby th'e ferrule I I. The ferrule II is provided with openings 3l topermit the gases in the expansion chamber incident to blowing of thefuse to escape from the interior of the fuse body. 'I'he openings 3l arecovered by a screen 32 which acts to retain the flame consequent to theblowing of the fuse while, at th'e same time, permitting the gases toescape.

In the modification shown by Fig. 3 the ferrule in the link end of thefuse ls likewise provided with openings 33 protected by a screen 34which confines the filler material within the tubular casing yet permitsthe gases formed by blowing of the fuse to escape through the opening 33from th'e interior of the casing.

When the fuse is subjected to a partial overload, for example, as inmotor starting, the fuse link I2 will heat up at the blow point II, butthe vlarge plug I6 will prevent the heating action from melting the fuselink at the blow point because it will absorb the heat from the fuselink and dissipate it over its radiating surface. However, if theoverloading is continued for more than a brief periodi' the plug will beunable to dissipate the heat as fast as it absorbs it from the fuse linkand consequently the plug will heat up, and the low melting point solder24 which unites the brass cup to the copper plug will melt, permittingthe spring 21 to separate the cup from the disk and thereby opening thecircuit through the fuse. 'Ihe spring 2'I acts to separate the cup fromth'e plug quickly and completely and retains the cup at a considerabledistance from the plug so that arcing between the plug and cup isprevented. In the event of a short circuit both the fuse link l2 and thelow melting point solder 24 will melt giving an instantaneousinterruption of the circuit by sepafuse link I2 will be absorbed to somedegree by the inner nller'material 23, but the excess gas pressures willrupture th'e frangible disk 2l permitting the gases'to' escape into theexpansion chamber 30 and thence through the screen 32 and openings ll tothe atmosphere. The disk is designed so that it will break immediatelyupon blowing oi the fuse thereby liberating the gas pressures andpreventing possible rupture of the casing I0. In some instances, forexample, with a very high current occurring over a short time intervalthe link I2, only, will blow, in which 'case the resultant gas pressureswill rupture or move the disk 2 I so that the gases will escape to' thechamber 30' v through the openings in the plug I6 and the cup I9. Thescreen I2 will catch any nller which may I be b1own through the opening2z and retain it m the expansion chamber 3l. In the modincation shown byFig. 3, the gas pressure may escape from the nller end oi the tube, aswell as from the expansion chamber, the openings 33 permitting passageof the gas while the screen 34 retains the filler withinthecasing I0.

It 'should be noted that diilerent ratings o'f the fuse may be obtainedby varying theradiating surface and mass of the plug I0,'the meltingpoint of the solder 24 and the area of the blow point I1 of the link.For example, a higher partial overload could be sustained by raising themelting point of the solder 24, or by increasing the radiating capacityof th'e copper plug I6. It will be apparent to one skilled in the artthat the three variables mentioned may be varied at will to design afuse oi any desired capacity wherein the plug acts to prevent partialoverload from blowing the fuse link. l

What I claim as new and desire to secure by Letters- Patent oi theUnited States, is:

l. In a fuse structure, afcasing, a fuse link in said casing, a plughaving an opening therein, said plug holding fsaidfuse in one end ofsaid l casing, and a disk covering said opening, said disk fuse torelease said pressure from said one vend of the casing.

3. In a time lag fuse, a casing, a perforated plug separating saidcasing into two compartments, a fusible link in one compartment fastenedto said plug, a cup in the other compartment, fusible material unitingsaid cup and plug, a disk covering said perforation andvdisposed'between said cup and said plug, and spring means acting I toseparate said cup and plug upon volatilization of said link and meltingof said material under overloadof said fuse whereby said cup and plugare separated and said disk is released to permit gas pressure `in saidone compartment to be released into said other compartment.

4. A time lag fuse comprising a casing, ferrules closing the ends of'said casing, there being openings in the ferrule at one end of saidcasing, a screen covering said openings, a tension spring. a cup, saidspring being connected at one'end to said vented ferrule and at theotherfend to said cup, a perforated element soldered to said cupv permitsaid spring'to retract said cup from engagement with said plug.

5. In a fuse structure, a casing, ferrules closing the ends of saidcasing, there being vent openings a plug having an opening thereinholding said in said ferrules, screens covering said openings, a fuselink connected at one end to one of said ferrules, a plug of relativelylarge mass connected to th'e other end of said link, a cup soldered toseparating said cup and plug upon melting of said v solder and saidvents liberating the gas pressures in said casing caused by blowing ofsaid fuse link. 6. In a time lag fuse, a casing, a perforated element insaid casing, a fusible link connected tol and element uponvolatilization of said link and melting of said material upon overloadof said fuse whereby said member and element are separated and said diskis shattered to release the gas j pressure incident to1 blowing of saidfuse.

` GEORGE R. BROWN.

